1. Field of the Invention
The present invention relates to a joint ring for an endoscope bending tube configured to fit with and to be fixed to a rigid member on a distal end side or a proximal end side in an axial direction, a bending tube of an endoscope including the joint ring, an endoscope, and a manufacturing method for the joint ring for the endoscope bending tube.
2. Description of the Related Art
On a distal end side of an insertion portion of an endoscope, a bending portion configured to be bendable and a distal end rigid portion, in which an illumination optical system, an objective optical system, and the like are disposed, are connected. The bending portion is configured by connecting a plurality of joint rings to be formed in a bendable structure. A first joint ring on a most distal end side is configured to fit with and to be fixed to a distal end rigid member in the distal end rigid portion on a distal end side in an axial direction. A last joint ring on a most proximal end side of the bending portion fits with and is fixed to a rigid member at a distal end of a flexible portion having flexibility on a proximal end side in the axial direction. Various techniques for performing positioning in fitting the first joint ring and the distal end rigid member (or fitting the last joint ring and the rigid member of the flexible portion) have been proposed.
For example, Japanese Patent Application Laid-Open Publication No. H11-56760, for example, FIG. 5, describes an endoscope in which a distal end fixed frame 32 incorporating an objective optical system and a first joint ring 40 disposed on a most distal end side among a plurality of joints configuring a bending tube connected to the distal end fixed frame 32 are butted against each other in an axial direction of an insertion portion, connected, and fixed, the endoscope including a plurality of cutouts 46 elongated in the axial direction formed in the distal end fixed frame 32, a convex portion 44 protrudingly provided on a distal end side of the first joint 40 and configured to engage with one of the cutouts 46 and perform positioning of the first joint 40 and the distal end fixed frame 32 in a circumferential direction, and a protrusion 45 protrudingly provided in a middle of a circumferential surface of the first joint 40 and configured to engage with a rear end face of the distal end fixed frame 32 and perform positioning of the first joint 40 and the distal end fixed frame 32 in the axial direction.
For example, Japanese Patent Application Laid-Open Publication No. 2008-188095 describes a technique for preventing deformation of a cylindrical portion, which is a joint ring main body, in applying pressing to a projecting portion for coupling joint rings each other. That is, the publication describes a joint ring for an endoscope including a cylindrical portion, an opposed pair of tabular first projecting portions provided to project in an axial direction of one end edge of the cylindrical portion, and an opposed pair of tabular second projecting portions provided at the other end edge of the cylindrical portion to project in the axial direction and located to shift in a radial direction of the cylindrical portion by one step with respect to the first projecting portion, the first projecting portion and the second projecting portion being superimposed each other and rotatably coupled by inserting a coupling pin through coupling holes respectively formed therein and a plurality of the coupled first and second projecting portions being connected in series to configure a bendable bending portion, wherein a slit is formed between the second projecting portion and the cylindrical portion. It is described that, since the second projecting portion and the cylindrical portion are separated in a part because the slit is formed between the second projecting portion and the cylindrical portion, it is possible to prevent flat deformation of the cylindrical portion and perform pressing of the second projecting portion and it is possible to press the second projecting portion with high flatness (see paragraph [0014] and FIG. 2).
Further, although a technical field is different from an endoscope, Japanese Patent Application Laid-Open Publication No. 2005-123085 describes a technique for, in a coupling portion of a joint portion 46 and an anode 86 of an X-ray tube device, by forming a taper surface 46P in the joint portion 46 and forming a torus-shape curved surface 86P in the anode 86, dispersing stress according to a shape characteristic of the curved surface 86P even when the anode 86 is heated and tensile stress to an outer side occurs in a coupling portion 86a (see paragraphs [0032] and [0033], FIG. 9, etc.).
Incidentally, when a joint ring of a bending tube of an endoscope is machined, plastic deformation such as bulge processing is sometimes used. Bulge processing means pressing for performing blow molding for, after setting a tube material in a mold, closing the mold and, for example, compressing both ends of a material in an axial direction while filling high-pressure liquid in the mold to thereby cause the material to flow while extending the material to have a shape formed in the mold. Bulge processing is also referred to as hydroforming.
A state in applying such bulge processing to a joint ring is explained with reference to FIGS. 23 and 24. FIG. 23 is a side view showing the joint ring before the bulge processing. FIG. 24 is a side view showing the joint ring after the bulge processing.
In forming, in the joint ring, a shape portion for fitting with a distal end rigid member and performing positioning, two ways are conceivable, i.e., forming the shape portion before performing the bulge processing and forming the shape portion after performing the bulge processing.
First, when the shape portion for positioning is formed after the bulge processing, to perform machining without causing deformation in the joint ring, it is necessary to hold a joint ring with a mold having a shape matching an external shape of the joint ring.
On the other hand, before the bulge processing is performed, since a tube material generally has a cylindrical shape, even when it is necessary to use a mold, a general-purpose inexpensive mold can be used. Alternatively, even if slight deformation occurs in the tube material before the bulge processing, the tube material can be formed in a predetermined shape if the bulge processing is performed thereafter. Therefore, it is also possible to adopt an option for machining the tube material without holding the tube material with the mold.
Because of such a reason, it is desirable that the shape portion for fitting with the distal end rigid member and performing positioning is formed in the joint ring before the bulge processing is performed.
Therefore, as shown in FIG. 23, a concave portion 108a for positioning is formed in a joint ring 108 before the bulge processing. The concave portion 108a is a concave portion for performing at least positioning in a circumferential direction using an end face 108b extending along an axial direction.
When the bulge processing is applied to the joint ring 108 shown in FIG. 23, tensile force for expansion in a radial direction around an axis acts on the joint ring 108. After the bulge processing, the end face 108b for performing positioning in the circumferential direction changes as shown in FIG. 24.